This proposal is aimed at expanding our knowledge of the psychological and physiological bases of meaning construction from scalp recordings of event-related potentials (ERPs) to words. Current evidence suggests that the N400 indexes the combined influence of semantic context and long term memory on word processing. The proposed studies examine these relations and use the N400 to address specific questions about language comprehension. Expts 1-8 aim to reveal which aspects of context facilitate processing, and how, by examining interactions of different language cues and effects of constraint. Expts 1-2 examine whether lexically-based associative priming is maintained across clause and/or verb phrase boundaries. Expts 3-5 examine whether compositional semantic constraints (from quantifiers) can override lexically-driven processes. Expt 6 focuses on interactions between discourse-level constraints and background knowledge elicited by an individual sentence. Expts 7-8 focus on whether constraint effects operate only on lexical integration or also affect lexical/conceptual access per se and whether they arise at conceptual levels, lexical levels or both. Expts 9-16 focus on the interaction between the lexical information associated with verbs and people's knowledge of the temporal and causal structure of events. Expts 9-11 norm materials. Expts 12-16 examine the processing of verbs denoting events that are causally- and temporally-related and examine how verb aspect affects the activation of event-specific knowledge in long term memory. Expts 17-23 use visual half field presentation to examine how the two hemispheres make use of context in real time and how they do(n't) use various language cues to access concept and event knowledge from long-term memory. Expt 17 tests the two hemispheres' sensitivity to message-level constraint. Expts 18-19 examine the hypothesis that the two hemispheres use message-level information differently with the RH driven by plausibility & LH by prediction. Expts 20-23 explore the hemispheres' sensitivity to various language cues providing information about event-structure. Expts 20-21 use adjectival participles to determine whether verb inflections quickly provide knowledge about events (typical participants & their roles), and if the hemispheres differ in this. Expts 22-23 examine the hemispheres' sensitivity to event-location information in general and to the prepositions that cue such information in particular. Given our interest in real time language processing we also propose to collect eye movement data in several experiments, to get a better sense of when eye movement and ERP measures complement, overlap or are inconsistent with each other. Overall, the proposed studies are aimed at determining how we combine information from the linguistic stream and from semantic memory to make sense of language as it unfolds in real time.